Applications of Auxetic Materials in Life Sciences

Auxetic materials are characterized by becoming thicker perpendicular to the applied force when stretched. This is caused by the way their particular internal structure is designed to deform and exhibit a negative Poisson's ratio. Scientists hope to exploit this effect to create new products, including body armor, joint replacements, stretchable electronics, electronic skin and more. 

Auxetic Materials and Meta-biomaterials

The term auxetic (from the Greek, auxetikos), means "that which tends to increase" and it's root word, auxesis, means "increase." 

Auxetic materials behave in an opposite manner to elastic materials. Robert Hooke, a contemporary of Sir Isaac Newton, is known for his law of elasticity: that the amount a material stretches is proportional to the force applied. Such stretching causes the material to get thinner.

In the case of auxetic materials, they get fatter when stretched. This technology can be applied across many industries:

• medical wound care, compression garments, smart bandages
• textiles smart fabrics, shoe fabric, long wear fabric
• safety solutions fire curtains, fire proofing, industrial safety solutions, safety performance solutions
• military blast/frag protection, tent materials

Development of Meta-biomaterials 

A metamaterial is defined as a material engineered to have a property that is not found in nature. (Meta is Greek for "beyond"). Meta-biomaterials are the biomedical variant of "metamaterials," and are made from assemblies of multiple elements fashioned from composite materials such as metals or plastics. 

In one example, research is ongoingly focused on finding a means of preventing loosening of hip implants. Using current technology, ten percent of hip implants done today will no longer be firmly fixated. Professor Amir Zadpoor at TU Delft believes he has found a solution utilizing an auxetic meta-biomaterial. Zadpoor and his colleagues are conducting experiments involving vertical pressure on an implant surrounded by a special foam with the mechanical properties of bone. As a result of this pressure, the new implant expands, compressing the surrounding bone. Clinical trials have yet to be done, but their hope is that the surrounding bone is stimulated to regrow and maintaining firm contact with the implant.

Advances in 3-D Bioprinting and Auxetic Materials

Research in the field of functional structures and bio-structures is rapidly advancing, with the development of practical applications using 3-D bioprinting. Simultaneous advances in medical imaging technologies in the past decade are enabling this. High-resolution 3-D image data provides indispensable support in the diagnosis and treatment of many diseases. 

3-D imaging also guides manufacturing of models of individual body parts. One goal of this research is the fabrication of medical phantoms, or mock-ups of a patient's body parts, to allow doctors or surgeons to visualize body parts when preparing, planning, or optimizing complex medical procedures or operations.

Another end use of 3-D bioprinting technology is for tissue engineering (TE) applications in order to build organs and body parts. Efforts continue to develop biological substitutes for native human tissue and organs, due to the increase in demand for tissue and organ transplantation and the lack of donors. Other advantages of using printed biodegradable scaffolds on which to support cellular growth are:

• eliminate tissue and organ rejection
• improve and accelerate the healing and repairing process
• provide a less-invasive treatment, with lower infection rates

Watch our video series about biomedical innovation.

Optimizing Auxetic Materials for Stretchability and Compressibility

Researchers are interested in the potential of mechanical metamaterials which offer enhanced flexibility in performance by coupling dynamically changing structural configurations with tunable physical properties. An emerging frontier is based on the art of paper cutting, called kirigami. Examples show that by introducing hierarchical line cuts into thin sheets of elastomer, researchers can generate "highly-stretchable, super-conformable, and ultra-soft configurations, which exhibit highly non-linear stress-strain behaviors resulting from the hierarchically cut structure rather than their constituent material."

They foresee broad potential applications:

• stretchable and conformable electronics
• optical tracking in solar cells
• stretchable energy storage devices
• acoustic filters
• 3-D mesostructures fabrication

Conclusion

The promise of creating versatile new auxetic materials continues to drive ongoing research, which will offer new options and advances in the medical and life sciences fields.